The invention relates to a device for control of the pressing period and for actuation of sealing jaws in conjunction with a packaging machine, especially for sealing of folding flaps of a packaging unit.
Packaging machines are provided with welding or sealing means, namely sealing jaws, if objects are to be wrapped in sealable foils or in packaging material provided with a sealable coating. In the manufacture of cigarette packets, one has to seal their outer wrapping of thermally-weldable foil, in the region of end faces, so that overlapping folding flaps are fixed together. For this purpose (heated) sealing jaws are installed, which maintain contact with the surfaces of the packets, i.e. of the folding flaps, during a defined time.
In order on the one hand to achieve sufficiently durable sealing of the folding flaps, but on the other hand to avoid damage to the foil by over-long action by the heated sealing jaws, it is necessary to control the pressing period of the sealing jaws accurately. The maintenance of exact, uniform sealing periods with predetermined pressure and specified temperature of the sealing jaws is made difficult in that the packages to be acted on may be transported with differing speeds. The reasons for this are variations in the cycle time, or number, of the packaging machine. Fundamentally, there are at least three different working regimes of the packaging machine which can be met in practice: the normal speed corresponds to the nominal output of the packaging machine, with cigarette packets e.g. 400 cycles per minute. For doing work on the packaging machine, especially for the removal of defective packets etc., a crawling speed is provided, in which the packaging machine runs with markedly reduced cycle number, e.g. at 200 cycles per minute. Then packaging machines are provided with a so-called overdrive, which provides cycle numbers above the normal speed for short periods.